In order to learn more about how synaptic vesicles are involved in the secretion of neurotransmitters, I propose to develop a method to abruptly freeze structural changes during secretion, by rapidly compressing living synapses in thin frog muscles between two cold metal surfaces. These isolated synapses will be subjected to various physiological and pharmacological stimuli in the moments before freezing, and visualized by the freeze-fracture technique, in order to view the sequence and timing of morphological changes in vesicle and plasma membrane during secretion, and to determine whether synaptic vesicle discharge through te plasma membrane is followed by a spatially and temporally separate vesicle retrieval from the plasma membrane. How cytoplasmic fillaments and intramembranous particles are involved in these membrane events will be investigated. BIBLIOGRAPHIC REFERENCES: Heuser, J.E., Reese, T.S. and Landis, D.M.D. L976. Preservation of synaptic structure by rapid freezing. Cold Spring Harbor Symposia on Quantitative Biology 40: l7-24. Basbaym, C.B. and Heuser, J.E. l976. Morphological studies of stimulated noradrenergic nerve terminals. Anatomical Record l84:354 (Abrastract).